Conditional scalacOptions with SBT - scala

Question

I am using a project with cross-build for Scala 2.8, 2.9 and (hopefully) 2.10, using SBT. I would like to add the -feature option when compiling with 2.10 only.
In other words, when I compile with a version smaller than 2.10.0, I would like to set the compiler options as:
scalacOptions ++= Seq( "-deprecation", "-unchecked" )
and when compiling with a version greater or equal than 2.10.0:
scalacOptions ++= Seq( "-deprecation", "-unchecked", "-feature" )
Is there a way to achieve this ?

Answer 1

I found this was quick and concise way of doing it:
scalaVersion := "2.10.0"
crossScalaVersions := "2.9.2" :: "2.10.0" :: Nil
scalacOptions <<= scalaVersion map { v: String =>
val default = "-deprecation" :: "-unchecked" :: Nil
if (v.startsWith("2.9.")) default else default :+ "-feature"
}

Answer 2

When cross-building, scalaVersion reflects the version your project is currently built against. So depending on scalaVersion should do the trick:
val scalaVersionRegex = "(\\d+)\\.(\\d+).*".r
...
scalacOptions <++= scalaVersion { sv =>
sv match {
case scalaVersionRegex(major, minor) if major.toInt > 2 || (major == "2" && minor.toInt >= 10) =>
Seq( "-deprecation", "-unchecked", "-feature" )
case _ => Seq( "-deprecation", "-unchecked" )
}

Answer 3

There is CrossVersion.partialVersion now which can be used for this. I am not sure which SBT it was introduced in, but it seems to work fine even in 0.13.8:
scalacOptions ++= {
if (CrossVersion.partialVersion(scalaVersion.value).exists(_ >= (2, 10))) {
Seq("-deprecation", "-unchecked", "-feature")
} else {
Seq("-deprecation", "-unchecked")
}
}
Note: you need to import scala.math.Ordering.Implicits._ to be able to use >= operator on tuples.